The accumulator device such as an electric double layer capacitor, a lithium ion secondary battery, or a lithium ion capacitor has an outer container which accommodates, in conjunction with an electrolytic solution, either an electrode unit having a plurality of positive electrode sheets and a plurality of negative electrode sheets alternately stacked one on another with a separator disposed therebetween, or an electrode unit with a positive electrode sheet and a negative electrode sheet stacked one on the other and wound with a separator disposed therebetween.
In the accumulator device, the positive electrode sheet is composed of, for example, to have an aluminum current collector on which an electrode layer containing a positive electrode active material is formed, while the negative electrode sheet is composed of, for example, to have a copper current collector on which an electrode layer containing a negative electrode active material is formed.
Furthermore, the outer container of the accumulator device is known to have mutually overlapped two outer films bonded air-tightly to each other at a bonding portion formed along the respective outer peripheral edge portions.
Furthermore, in the accumulator device having such an outer container, a plate-shaped positive electrode terminal electrically connected to the current collector of the positive electrode sheet and a plate-shaped negative electrode terminal electrically connected to the current collector of the negative electrode sheet are provided so as to protrude from inside the outer container to outside the outer container through the bonding portion.
Conventionally, the positive electrode terminal used was made of aluminum or made up of an aluminum terminal substrate on the surface of which a nickel-plating coating is formed, while the negative electrode terminal used was made of copper or nickel (See Patent Literature 1 and Patent Literature 2).